Thermo-plastic molding machine with floating screw spreader



Oct. 22, 1968 D. A. DRAUDT ET AL 3,406,429

THERMO-PLASTIC MOLDING MACHINE WITH FLOATING SCREW SPREADER INVENTORS/Vf fl? @40g BYm/fy uw wid/M W J M Oct. 22, 1968 D. A. DRAUDT ET A1.3,406,429

THERMO-PLASTIC MOLDING MACHINE WITH FLOATING SCREW SPREADER 4Sheets-Sheet 2 Filed May 19, 1966 INVENTORS` W57 Oct. 22, 1968 D- DRAUDTET AF: 3,406,429

' THERMO-PLASTIC MOLDING MACHINE WITH FLOATING SCREW SPREADER Filed May1,9, 1966 4 Sheets-Sheet 5 INVENTORS Hf/@f f www@ M?! N" MM, i. Q i fm;

Oct. 22, 1968 D. A. DRAUDT ET AL f 3,406,429

THERMO-PLASTIC MOLDING MACHINE WITH FLOATING SCREW SPREADER Filed May19, 1966 4 Sheets-Sheet. 4.

INVENTORS $57555? "gm/wpd.) K. m .1M

United States Patent O "Ice 3,406,429 THERMO-PLASTIC MOLDING MACHINEWITH FLOATING SCREW SPREADER Donald A. Draudt, 27180 Pompton Drive, andHerbert T.

Draudt, 28520 Lynhaven, both of North Olmsted,

Ohio 44070 Filed May 19, 1966, Ser. No. 551,386 7 Claims. (Cl. 18-30)This invention relates to injection molding machinery for the productionof molded plastic articles.

More particularly our invention relates to an improved machine forplasticizing moldable material and injecting a measured charge thereofinto a mold cavity.

Injection molding machines are used to form many types of plasticmaterials, especially thermoplastics such as nylon, polyethylene, vinyl,styrene, polyurethane, Delrin and acetate. Where thermoplastics areused, the machine can be cycled as fast as the material can be heatedand plasticized in the cylinder and a measured charge thereof positionedfor injection. Operating limitations are largely those imposed by themolds themselves. Fast cycling is particularly desirable in order toavoid overheating and charting, or heating of portions or zones `ofmaterial for an excessive period of time sufficient to causedecomposition.

Means for obtaining this result, however, have not been satisfactory inthe prior art practices for several reasons.

In many cases rapid cycling of the injection molding equipment fails toachieve complete and/ or homogeneous mixing of the plastic materialprior to injection so that the resulting molded product tends to have anuneven texture and/or appearance. Also the injection mechanism does notremove all of the material in the charging end or forward end of thecylinder during the molding cycle. As a result, residual material mayremain in the cylinder in a heated condition for a time period that mayexceed its physical limits and may become charred, or in some casesdecomposed. As a result frequent cleaning of the cylinder bore isrequired, or the faulty material flakes off and gets into the moldedproduct.

Some current and prior injection molding machines utilize a rotating andreciprocating screw with complicated valving at the forward end whichoperates during the injection and retraction movements. Such valvingpermits forward movement of the material in the cylinder duringretraction of the piston or screw but closes to prevent rearwardmovement of material dur-ing the injection stroke. The use of suchvalves further complicates the problem of cleaning the cylinder andincreases the possibility of malfunction of the machine. Also, due tothe viscosity of the plasticized material the opening and closing isrelatively sloppy and cannot be relied -upon to provide a measuredcharge for injection.

An additional drawback of the rotating and reciprocating Screw typemachines is `that the shaft of the screw is at times caused to flex orbend due to the high pressures generated d-uring the injection stroke.The flexing occurs when a force is applied to the rearward end of thescrew shaft to force the screw axially forward against the plasticizedmaterial to be injected. This affects the operation of the machineadversely and tends to cause breakage.

Another objectionable feature of prior equipment is that excessivepressures maintained on the plastic material in the mold after it isfilled causes undesirable in-ternal stresses in the molded product.While a high injection pressure is needed during most of the injectionstroke in order to overcome the viscosity resistance of -the material`and to compensate for shrinkage in the mold, once the mold is filled,pressure in excess of that needed to offset shrinkage tends to result inflash as well as deleterious 3,406,429 Patented Oct. 22, 1968 stress inthe product. Some prior techniques for reducing the pressure in the moldat and/or near the end of the injection stroke, have required complexpressure sensing devices and valve actuated pressure release mechanisms,'ld have not been effective nor free from wear and trourI`he apparatusof our invention overcomes the objections mentioned above and affordsother features and advantages heretofore long desired, but not obtained.

The preferred embodiment of our invention provides a plasticizingcylinder having a bore with an input or rearward end, and an injection,or forward, end. Mounted for free axial movement in the bore of thecylinder is a rotatable member having a screw portion intermediate itsends. A rotary drive means sl-idably engages the rotary member to permitfree axial movement of the member during its rotation as well as duringperiods of nonrotation. Also mounted within the cylinder bore isaplunger which is mounted for reciprocating movement within and -adjacentthe input end of the bore in the space between the wall of the bore andthe rotary member. The plunger serves both to close the inlet to thebore and to press the plastic material confined in the bore along withthe rotatable member, axially forward toward the injection end of thebore to force material out of the injection nozzle, the plunger 'beingreciprocated by -a suitable drive means.

In one embodiment of our invention the mechanism described above is usedin connection with an injection apparatus having means for moving theinjection nozzle into and out of communication with the mold sprue, themeans being the same as that used to reciprocate the plunger.

According to another aspect of our invention the rotatable memberincludes in addition to the screw portion, a mixing head at the forwardend thereof which has longitudinal ribs serving to homogenize a measuredcharge of plastic material at the forward end of the cylinder bore andwhich bot-toms at the end of the bore near the end of the injectionstroke so that the injection pressure is substantially reduced at andbeyond the end of the bore, in anticipation of any flash from the mold.The ribs are adapted to engage the end walls of the cylinder bore duringrotary movement of the mixing head, and thus tend to remove or moveresidual plasticized material from the walls after each injectionstroke.

It is 'among the objects of our invention to provide a new and improvedinjection molding `apparatus which affords a more effective heating andmechanical working of the molding material and improved control ofpressure, volume and temperature of the injected material.

Another object of our invention is to provide an injection moldingapparatus which rapidly `and positively fills the mold withhomogeneously mixed plasticized material and then maintains anadvantageously reduced holding pressure on the injected material whilethe material Yshrinks and solidifies in the mold. Similarly, it is amongour objects to avoid flash from the mold, and lavoid harmful compressionstresses in the injected material in the mold.

Another object of our invention is to avoid the use of valving of anytype in the reciprocating injection mechanism .within the cylinder.

A further object of our invention is to remove residual material fromthe forward end of the injection cylinder during each cycle to preventoverheating and charring of the plasticized material.

Other objects of our invention are to provide an accurate and readilyadjustable measure of the plasticized charge of material to be injectedinto the mold, to remove air from unplasticized material in thecylinder, to avoid flexing or excessively stressing of the screw shaft 3and take better and/or exclusive advantage of the screw in its functionsof mixing and measuring the material to be injected. v

Other objects, uses and advantages of our invention will become apparentfrom the following detailed description of a preferred form, referencebeing had to the accompanying drawings wherein:

FIGURE 1 is a sectional view taken through the cente of an injectionmolding apparatus embodying the invention;

FIGURE 2 is a side elevational view of the apparatus of FIGURE l withparts broken away l.and shown in section, the plunger carrier platebeing shown in its downward position at the end of an injection stroke;

FIGURE 3 is a side elevational view similar to FIG- URE 2 with partsbroken away and shown in section, the plunger carrier plate being shownin its uppermost position, and the rotary member in its most rearwardposition preparatory to an injection stroke; y

FIGURE 4 is a fragmentary cross-sectional view taken on the line 4 4 ofFIGURE l showing the rotary member of the apparatus in its forwardposition following an injection stroke and the cylinder and nozzlelifted out of communication with the mold sprue;

FIGURE 5 is a fragmentary sectional view similar to FIGURE 4 showing therotary member of the apparatus in its rearward position preparatory toan injection stroke; and

FIGURE 6 is a fragmentary sectional view similar to FIGURES 4 and 5showing the condition of the apparatus during an injection stroke; and

FIGURE 7 is a fragmentary sectional view similar to FIGURES 4, 5 and 6showing the forward end of the rotary member bottomed against the end ofthe cylinder and the plunger in its most forward position during theiinal portion of an injection stroke.

The apparatus Referring -more particularly to the drawings there isshown an injection molding apparatus A embodying the invention, andad-apted for use in connection with a closeddie mold B best shown inFIGURES 2 and 3. The apparatus A includes a frame C, a feed-hopper Dmounted on the frame C, and a cross-member E. The cross-member Esupports the working parts of the apparatus and has bearings providedlat its opposite ends which are carried in the frame C so that it iscapable of pivotal movement. This method of mounting facilitatescleaning of the equipment and changing of parts.

Mounted on the cross-member E are two hydraulic cylinders 11 and 12having piston rods 13 and 14 extending downwardly through thecross-member. Connected to the piston rods 13 and 14 is -a plungercarrier plate l5 which carries a tubular injection plunger 16. 'I'heplunger carrier plate 15 is guided for reciprocating movement by guiderods 17 and 18 which are mounted in fixed position on the cross-memberE. Mounted below the plunger carrier plate 15 is `a cylinder carrierplate 20 which is guided for reciprocating movement on the guide rods 17and 18 and which supports a plasticizing cylinder 21 having -aninjection nozzle 22 at its lower end. The cylinder carrier plate iselective to move the plasticizing cylinder 21 and the injection nozzle22 between the positions shown in FIGURE 2 wherein the bottom of thecylinder 21 rests on a block 23 mounted at the bottom of frame C, and aposition wherein the cylinder 21 and injection nozzle 22 are liftedupward to bring the nozzle 22 out of communication with mold sprue aswill be more particularly described below.

Movement of the plasticizing cylinder 21 is accomplished by means oflifter -rods 24 and 25 mounted at opposite ends of the cylinder carrierplate 20. The lifter rods 24 and 25 extend upwardly from the cylindercarrier plate 20 and through bushings 26 and 27 located in the plungercarrier plate 15. The upper ends of the lifter rods 24 and 25 have aradial flange 28 which overlies the 4 top surface of the plunger carrierplate 15 so that during the terminal portion of the upward movement ofthe plunger carrier plate 15 the lifter rods 26 and 27 are pulledupwardly to raise the cylinder carrier plate 20 together with theplasticizing cylinder 2.1.

`Mounted on the cylinder V'carrier plate 20 above theplasticizingcylinder 21 is a guide bushing 29 which receives the tubularinjection plunger 16 and guides its reciprocating movement. The bushing29 also serves to close the upper end of the plasticizing cylinder 21.

Mounted for free axial movement within the plasticizing cylinder 21 is arotary member 30 having a shaft 31 which extends upwardly from theplasticizing cylinder 21, through the tubular injection plunger 16, andthrough the plunger carrier plate 15 and cross-member E. The outer end32 of the shaft 31 is splined and is engaged by a rotary hydraulic driveunit 33. The splined outer end 32 is so designed that the rotary member30 is capable of free axial movement during operation of the rotarydrive. Located at the lower end of the rotary member 30A within the bore3S of the plasticizing cylinder 21 is a screw portion 36 having a minordiameter which increases gradually from rear to front as best shown inFIGURES 4 through 7. At the lower end of the rotary member 30 adjacentthe screw portion 36 is a mixing head 37 having radially extending ribs38.

The plastic material to be molded is supplied in dry solid form such aspowder or granules to the cylinder bore 35 from the hopper D by means ofan annular inlet port 34 formed in the cylinder carrier plate 20 betweenthe upper end of the plasticizing cylinder 21 and the guide bushing 29.During the operation of the equipment the tubular injection plunger 16moves downwardly into the cylinder bore 35 and closes off the feed port34 as best shown in FIGURES 6 and 7.

On the side of the cylinder carrier plate 20 opposite the hopper D is aclean-out space 39 normally covered by a plate 40. The space 39communicates with the bore of the plasticizing cylinder so that theupper end of the bore and the port may be periodically cleaned whendesired.

It will be noted that the rotary member 30, the tubular injectionplunger 16 and the plasticizing cylinder 21 are all movable linearallyrelative to one another. Reciprocating movement of the plasticizingcylinder 21 and attached injection nozzle 22 between the position shownin FIG- URES 4 and 5 and the position shown in FIGURES 6y and 7 isprovided for by means of the lifter rods 24 and 25 as described above.

When the nozzle is in the position shown in FIGURES 6 and 7, the port 45of the nozzle communicates with the sprue 46 of the mold. The nozzleport 45 communicates with the lower end of the cylinder bore 35 by meansof a passage 47 formed in the plasticizing cylinder 21 to permitplasticized material to flow from the bore to the nozzle and then intothe mold cavity. The flow of fluid from the nozzle to the mold ma'y beinterrupted during the molding cycle by lifting the plasticizingcylinder 21 and nozzle 22 upward to the position shown in FIGURES 4 and5. In this position the mold block seals the nozzle port 45 and preventsescape of material.

Movement of the tubular injection plunger 16 between the position shownin FIGURES 4 and 5 that shown in FIGURE 7, is accomplished by means ofthe plunger carrier plate 15 and the hydraulic cylinders 11 and 12.

Axial movement of the rotary member 30 is accomplished by twoindependent means. With reference to FIG- URES 4 and 5, the rearwardmovement of the member 30 from the position shown in FIGURE 4 to theposition shown in FIGURE 5 is accomplished by rotating the membercounter-clockwise in a manner tending to move the screw portion 36rearwardly relative to the cylinder bore 35 and to push materialforwardly from rearward of the screw portion 36 to the mixing head 37.During this rotary movement dry solid material entering through theinlet port 34 is fed forwardly by the screw threads. Because the minordiameter of the screw portion increases gradually from rear to front thedry material is eventually compacted and squeezed outwardly against theinner wall of the bore 35 as it rea'ches the lower end of the screwportion 36, the mixing head 37 serving to further mix and homogenize thematerial. Sufficient clearance is provided between the screw threads andthe wall of the bore that material which is squeezed between the threadsand the bore will not absorb too much heat and be charred. A clearanceof about .06 inch has been found suitable for many applications.

Both the plasticizing cylinder 21 and the nozzle 22 are heated by anexternal electrical heating jacket 48 during the operation of theequipment to provide desired plasticizing temperatures as is well knownin the art.

The rotary movement of the screw portion 36 develops a pressuredifferential between the plasticized material at the forward end of thebore and the material rearward of the screw threads so that the rotarymember 30 is forced rearwardly to the position shown in FIGURE 5. Inthis position a measured charge of plasticized material is located inthe spa'ce forward of the mixing head. The volume of this space may beadjusted by limiting the upward movement of the rotary member. Operationof the rotary drive unit 33 is stopped in response to actuation of alimit switch 50 which is engaged by the outer end 32 of the shaft 31after the rotary member has been lifted to the desired height as shownin FIGUR-E 5.

Downward movement of the rotary member 30 is accomplished by means ofthe tubular plunger 16 which presses against the material at the upperend of the cylinder bore 35 adjacent the inlet port 34 and forces boththe material and the rotary member 30 downwardly through the bore. Thisserves to force plasticized materia'l located at the lower end of thebore outwardly through the passage 47 and the nozzle port 45 into themold B through the mold gate 46.

The mixing head 37 bottoms against the lower end of the cylinder bore 35as shown in FIGURE 7, however the ribs 38 keep the body portion of themixing head 37 from closing the outlet passage 47 in the cylinder andthe uid pressure developed in the material in the mold cavity isrelieved and balanced against the reduced fluid pressure of the materialin the cylinder 21. The tubular plunger \16 travels slightly in itsdownward direction even after the mixing head bottoms so that somematerial is squeezed in a helical path of travel through the roots ofthe screw portion 36.

Because the fluid pressure in the mold cavity is relieved somewhat afterthe mixing head bottoms, overstressing of the plastic material in themold cavities is prevented although sufficient pressure is maintained bythe plunger 16 to compensate for shrinkage as the material cools. Alsothe engagement of the lower end of the cylinder bore 35 by the ribs 38of the mixing head 37 of the st-roke enables the ribs to wipe residualmaterial from the lower surface of the bore when rotation of the rotarymember is begun preparatory to its retraction movement. This preventsthe decomposition of the residual material which would otherwise resultdue to the high temperatures maintained in the cylinder wall by theexternal heating jacket 48. The lower limit of downward travel of theinjection plunger 16 is variable and depends upon the back pressuredeveloped by the material in the bore 35. The hydraulic cylinders at 11and 12 develop consistent pressures during each stroke regardless of theposition of the plunger 16.

The cylinders 11 and 12 are actuated to pull the plunger 16 upwardly outof the cylinder bore to the position shown in FIGURE 4, shortly afterthe mixing head 37 bottoms. During the last portion of the upwardmovement of the -plunger the radial flanges 28 at the ends of the lifterrods 24 and 25 are engaged by the plunger carrier plate 15 to lifttheplasticizing cylinder 21 and Operation The operating cycle of theinjecting molding apparatus shown and described may be best understoodby reference to FIGURES 4 to 7. Before the equipment is used inconnection with a specific mold and a specific material,

vthe timing between the various portions of the cycle and the strokelengths of the plunger 16 and the rotary member 30 should be carefullyadjusted. The dwell time in which the mold B remains closed after theplastic material has been injected should be suiicient to permitsuitable cooling of the material. Also the time period ybetween thrustand retraction movements of the hydraulic cylinders 1 and 2 must becarefully adjusted. Additionally the temperatures maintained by theheating jacket 48 of the plasticizing cylinder and injection nozzleshould be adjusted for the particular plastic material being used andshould be very carefully thermostatieally controlled.

Considering the cycle as beginning with the apparatus in the conditionshown in FIGURE 4, the nozzle being out of communication with the moldsprue, the rotary drive unit 33 for the rotary member 30 is actuated,usually by a control system utilizing timers to coordinate the cyclewith the opening and closing of the mold. As the screw portion 36 of therotary member 33 is forcibly rotated, the material is homogenized,compacted in `the roots of the threads and eventually forced to theforward space of the cylinder bore 35. As material in plasticized formadvances forwardly of the screw portion 36 it is further mixed andhomogenized by the ribs 38 formed on the mixing head 37. As the materialis compacted, squeezed :and homogenized, more material is drawn inthrough the inlet port 34 at the upper end of the cylinder from thehopper D.

Due to the compaction and squeezing of the material, several revolutionsof the rotary member aire normally required for the member to moveaxially the equivalent of one pitch length, the rearward movement tbeingprimarily dependent upon the dilference in pressure between the materialrearward of the screw portion and the material in the forward end of thebore.

After the rotary member has been raised to a pre-set upper limit such asshown in FIGURE 2, the limit switch 50 is actuated to stop the rotarydrive unit 33. The hydraulic cylinders 11 and 12 are then actuated andbegin to force the plunger carrier plate 15 downward. The initialportion of this downward movement lowers the cylinder carrier plate 20until the bottom of the plasticizing cylinder 21 engages the block 23.This moves the nozzle port 45 into comunication with the mold sprue 4'6to permit the plasticized material to flow from the space in the forwardend of the cylinder bore 35 to the mold cavity. As indicated above ameasured charge of plasticized material is at this point located in theforward space of the cylinder bore 35. The downward movement of theplunger carrier plate 15 and the injection plunger l16 is continued asshown in FIGURE 6 and the inlet port 34 is closed. The pressure beingexerted against the material rearwardly of the screw portion 36 iseffective to drive .the rotary member 30 downwardly :along with theplunger 16. This serves to force the measured charge of plasticizedmaterial out of the forward space and into the mold cavity. Toward theend of the injection stroke the ribs 38 of the mixing head 37 bot-tomagainst the forward end surface of the cylinder bore 35. The downwardmovement of the plunger 16 however tends to continue until the pressureexerted on the plunger carrier plate is counter balanced by the pressureof the plastic material 7 rearwardly of the screw portion 36 of therotary member 30. When these pressures equalize, the downward stroke ofthe plunger is stopped. Since the lower end of the mixing head isbottomed against the end of the cylinder bore the pressure in thematerial is reduced as the filling of the mold cavity is completed andas the material cools and shrinks. The time period in which theapparatus remains in this condition is preferably controlled by a timerand is dependent primarily on the particular material being used.

After a suitable time delay the hydraulic cylinders 11 and 12 retractthe injection plunger 16 from the cylinder bore 35. This movement of thepiston rods 13 and 14 serves two purposes as indicated above. Inaddition to retracting the plunger 1'6 from the cylinder bore 35 andopening the inlet port 34, the plasticizing cylinder 21 and the nozzle22 are raised relative to the mold to the position shown in FIGURE 4.With the equipment in this condition the rotary drive unit 33 havingbeen actuated 'by the limit switch 51, after a pre-set time delay, turnsthe rotary member 30 to feed a new measured charge of plasticizedmaterial into the forward space of the cylinder bore as described above.Then the mold may :be opened to remove the molded part. Once themeasured charge has been provided the mold is closed and the cylindernozzle dropped into the position shown in FIGURE 2 so that anotherinjection stroke may be commenced.

It will be understood that our invention has been shown and describedwith reference to a preferred embodiment thereof which is intended forthe purpose of illustration rather than limitation, and that variationsand modifications will be apparent to those skilled in the art withinthe intended spirit and scope of our teaching, wherefor We do not wantour patent to be limited to the form or forms of method or apparatusherein specifically illustrated and described nor in any mannerinconsistent with the progress by which the art has been promoted by ourinvention.

We claim:

1. Apparatus for injecting plastic material into a mold comprising aplasticizing cylinder having a bore with a rearward feed end and aforward outlet end, a rotatable member mounted for free axial movementand having a screw portion adapted to work plastic material in saidbore, means for turning said rotatable member in a manner tending toscrew said member axially rearwardly through said material in said bore,a plunger mounted for reciprocating movement relative to said bore andsaid member, adjacent the feed end of said bore, and adapted to pushplastic .material forwardly in said bore and induce said screw portionto move forwardly with said material toward the outlet end of said bore,and means for reciprocating said plunger in said bore.

2. An apparatus as defined in claim 1 wherein said rotatable memberincludes a mixing head forwardly of said screw portion, said mixing headhaving ribs which antenas 8 bottom against the outlet end of said borewhereby space is provided to permit a limited owof material from theoutlet end of said bore whensaid mixing head is bottomed.` 4

3. An apparatus as defined in claim 1 including an in. jection nozzlemounted on said cylinder and adapted to engagea mold vsprue', saidnozzle having a port communicating with the outlet end of said bore,said cylinder and nozzle being adapted for reciprocating movementbetween a position wherein said port communicates with said mold sprueand a position wherein said port is sealed by a surface of said, mold,said cylinder and nozzle being reciprocated by said meansforreciprocating vsaid plunger in said bore.

4. Apparatus as defined in claim 3 wherein said means for reciprocatingsaid plunger and said plasticizing cylinder comprises a first slidablemember carrying said cylinder4A and biased to a position wherein saidnozzle port communicates with said ,mold sprue, a second slidable membercarrying said plunger and located rearwardly of said first member,connecting means mounted on said first member and extending through saidsecond member, said connecting means being slidable relative to saidsecond member and having an enlarged outer end portion adapted to engagesaid second member and at least one hydraulic cylinder having areciprocating piston rod connected to said second member to operate saidplunger whereby dur. ing rearward movement of said plunger, said secondslidable member engages said enlarged portion of said connecting meansand carries said first slidable member and said Ycylinder and nozzlerearwardly to move said nozzle to a position wherein said nozzle port issealed by said mold.

5. An apparatus as defined in claim 1 including means responsive to saidrearward motion of said member to stop the turning thereof.

6. An apparatus as dened in claim 1 including means responsive to saidrearward motion of said member to initiate forward movement of saidplunger.

7. An apparatus as dened in claim 1 including means associated with theforward end of said rotary member for ythrottling the outflow ofmaterial from the cylinder when the mold cavity is substantially filledwith the injected material.

References Cited `UNITED STATES PATENTS WILBUR L. MCBAY, PrimaryExaminer.

1. APPARATUS FOR INJECTING PLASTIC MATERIAL INTO A MOLD COMPRISING APLASTICIZING CYLINDER HAVING A BORE WITH A REARWARD FEED END AND AFORWARD OUTLET END, A ROTATABLE MEMBER MOUNTED FOR FREE AXIAL MOVEMENTAND HAVING A SCREW PORTION ADAPTED TO WORK PLASTIC MATERIAL IN SAIDBORE, MEANS FOR TURNING SAID ROTATABLE MEMBER IN A MANNER TENDING TOSCREW SAID MEMBER AXIALLY REARWARDLY THROUGH SAID MATERIAL IN SAID BORE,A PLUNGER MOUNTED FOR RECIPROCATING MOVEMENT RELATIVE TO SAID BORE ANDSAID MEMBER, ADJACENT THE FEED END OF SAID BORE, AND ADAPTED TO PUSHPLASTIC MATERIAL FORWARDLY IN S AID BORE AND INDUCE SAID SCREW PORTIONTO MOVE FORWARDLY WITH SAID MATERIAL